1. Field of the Invention
This invention concerns an improved system for determining the quantity of a fuel stored in a tank subject to varying external forces, and particularly to the quantity of gasoline stored in an automobile gas tank.
2. Description of the Related Art
The present invention is an improvement on the invention disclosed in U.S. Pat. No. 5,133,212 to Grills et al., the contents of which are included herein by reference. Grills et al. disclose a weighing system utilizing a plurality of load cells supporting the fuel tank and a reference weight and load cell which, in combination with the tank load cells, corrects automatically for the external forces acting on the tank to give an accurate average measure of the quantity of liquid in the tank. Although this system is quite accurate and finds its best use where the cost of such a system can be justified, such as in measuring the quantity of fuel in an airplane fuel tank, the complexity of such a system is not justified where cost is of relatively greater importance such as in the determination of the amount of fuel in an automotive fuel tank.
Another tank weighing system which does not use load cells is disclosed by Kitagawa et al. in U.S. Pat. No. 4,562,732 where the tank is supported on one side by a torsion bar system. In contrast to Grills et al., although the Kitagawa et al. device is quite complicated and consequently quite expensive, it contains no system for correcting for the roll or pitch motions of the vehicle other than to average the tank readings over an extended period of time.
The external forces acting on an automobile fuel tank due to turning, roll and pitch although significant are much less severe in an automobile than in an airplane. Forces due to pitch generally arise when a vehicle is climbing or descending a hill which in North America rarely exceeds 15 degrees and only occasionally exceeds 5 degrees. Roll angles of more than 5 degrees are similarly uncommon. Even when steep angles are encountered, it is usually only for a short time. This is not generally the case in aircraft, especially high performance military aircraft, where turning pitch and roll related forces are not only greater in magnitude but can last for an extended period of time.
The most common systems of measuring the quantity of fuel in an automobile fuel tank use a variable resistance rheostat which is controlled by a float within the gas tank. This system makes no attempt to correct for external forces acting on the tank or for the angle of the vehicle. Modern gas tanks have a convoluted shape and the level of fuel is frequently a poor indicator of the amount of fuel within the tank. In many implementations, for example, the gage continues to register full even after several gallons have been consumed. Similarly, the gage will usually register empty when there are several gallons remaining. It is then a guessing game for the driver to know how far he can go before running out of gas.
The problem has been compounded with the implementation of a digital fuel gage display where the driver now gets an inaccurate display, with seemingly great precision, of the amount of fuel used and amount remaining in the tank. If, for example, the gage states that 14.5 gallons have been consumed and the driver has the tank filled and notices that it takes 15.3 gallons to fill it he wonders if he is being cheated by the service station or, as a ninimum, he begins to doubt the accuracy of the other gages on the instrument panel. The inaccuracy of the fuel gage is now the most common complaint received by at least one vehicle manufacturer from its customers.
These prior art float systems arc also vulnerable to errors due to fouling of the resistor induced by he necessity to operate the sensing elements in direct contact with the mixture held in the tank. These errors can cause the system to become inoperative or to change its calibration over time. These and other problems associated with the prior art fuel gages are solved by the present invention as disclosed below.
Reference is also made to U.S. Pat. No. 4,890,491 (Vetter et al.) which describes a system for indicating the level of fuel in an automobile tank (FIG. 4) which includes a fuel level detector 1, a detector 24 for detecting the longitudinal inclination of the vehicle, a detector 25 for detecting the transverse inclination of the vehicle and a microcomputer 26 containing a table providing an xe2x80x9cimmersion characteristic curvexe2x80x9d. In operation, the microcomputer 26 receives input from the fuel level detector 1 and inclination detectors 24,25 and corrects the level of fuel as measured by the fuel level detector 1 in light of the transverse and longitudinal inclination of the vehicle as measured by the detectors 24,25 by the application of the immersion characteristic curve to avoid false readings caused by inclination of the vehicle. Vetter et al. does not take any readings during periods of inclination of the vehicle during operation thereof nor provide a corrected level of liquid.
Reference is also made to U.S. Pat. No. 4,815,323 (Ellinger et al.) which describes a fuel quantity measuring system having ultrasonic transducers for measuring volume of fuel in a tank. In the embodiment shown in FIG. 1 (but not the embodiment shown in FIG. 2), the system includes ultrasonic tank sensor units which provide a signal representative of the round-trip time between each sensor to the surface of the full, a processor unit (CPU) which receives the round-trip time (which is proportional to the height level of fuel in the tank) and a display to display the volume of fuel in the tank. In this embodiment, the processor is described as performing height-volume calculations and then correcting for attitude, i.e., the pitch and roll of the vehicle. As such, it is clear that for this embodiment, the measured round-trip time is applied to the height-volume table to obtain a volume corresponding to that round-trip time. This volume estimation is thereafter corrected based on the attitude, i.e., the measured pitch and roll. In the embodiment in Ellinger et al. FIG. 3, the tank 12 includes three ultrasonic transducers 14,16,18 which send a respective signal representative of the round-trip time to the surface of the fuel 10 in respective stillwell 22 each surrounding that transducer to a computer 28 through a multiplexer 34. Only one transducer is related to fuel level (see FIG. 2) and the other two transducers are related to reference purposes and fuel density. The computer 28 has a memory 30 which it appears contains height-volume tables specific to each location of the transducer so that the measured round-trip time representative of the height level of fuel at that sensor location can be converted into a volume measurement. Thus, in this Ellinger et al. embodiment, the height of the level of fuel in the tank at each different location is converted to a volume measurement based on the height-volume tables. However, in this embodiment, there is no disclosure of the converted volume measurements being corrected by an attitude correction factor, i.e., the pitch and roll angles of the vehicle.
The fuel gage of the present invention uses a combination of (i) one or more load cells or fuel level measuring devices, plus in some cases other sensors which measure the pitch or roll angle of the vehicle or the fuel density, to approximately measure the quantity of the fuel in the tank and (ii) a processor and algorithm to correct for the inaccuracies arising from the pitch and roll angles of the vehicle, other external forces or from variations in fuel density. Although several weighing systems are disclosed for illustrative purposes, the invention applies to any method of making an approximate measurement of the fuel quantity and then using analytical techniques to improve on the measurement.
The principle objects of this invention are:
1. To provide a measuring system for determining the quantity of fuel in a fuel tank of an automotive vehicle operating on land that is subject to accelerations and pitch and roll rotations.
2. To provide analytical methods using a processor and algorithm and the output from one or more transducers for accurately determining the quantity of fuel in an automobile fuel tank when the tank has a complicated geometry.
3. To provide a simple, low cost system using a capacitance with fuel as a dielectric to determine the level of fuel in the tank.
4. To provide for a simple correction for the effects of pitch and roll in the tank weighing system through the use of an empirically or analytically derived relationship between the individual load cell readings and the weight of fuel in the fuel tank.
5. To provide for a correction for the effects of pitch and roll through the use of pitch and roll angle sensors and an empirically or analytically derived relationship between transducer readings and the quantity of fuel in the tank.
6. To eliminate the errors on automobile tank weighing systems caused by the accumulation of mud or ice on an exposed tank.
7. To eliminate the errors on automobile tank weighing systems caused by the variations in fuel density.
8. To provide a variety of low cost load cell designs for use in tank weighing systems.
9. To provide a method of increasing the accuracy of the currently used float fuel gages.
10. To provide for a more accurate fuel level gage.
Among the believed novel aspects embodied in the present invention is that a system, constructed in accord with the present invention, can use a variety of different fuel measuring transducers which by themselves give an inaccurate measurement of the quantity of fuel in the tank but when combined with an empirically derived algorithm results in a highly accurate fuel quantity measurement system. These transducers can be weight measuring load cells, vehicle angle measuring transducers, or fuel level measuring devices based on either float, ultrasonic or capacitive measurement devices.
When load cells are used they arc aligned to be sensitive generally parallel along an axis substantially normal to a horizontal plane and generally parallel to the yaw or vertical axis of the vehicle. A microprocessor with analog-to-digital converters converts the analog signals into output information representative of the volume or level of the liquid in the fuel tank by a variety of techniques but all employing the use of an algorithm which is based on empirical or analytical approximation techniques to relate the quantity of fuel in the tank to the measured quantities.
Although a number of the systems disclosed and illustrated below make use of a number of weight measuring devices for illustration, the invention is not the use of weighing per se but the use of one or more of a variety of transducers including load cells, angle gages, and level gages in combination with an algorithm and processor to determine the quantity of fuel in the tank with greater accuracy than can be obtained from a single transducer alone.
In one basic embodiment of the method in accordance with the invention, a plurality of measurements are conducted, each including the value of at least three parameters concerning the tank and the known volume of the tank selected from the group consisting of the load of the tank on a load cell arranged at a first location, the load of the tank on a load cell arranged at a second location, the load of the tank at a load cell arranged at a third location, the pitch angle of the vehicle, the roll angle of the vehicle, the height of the fuel at a first location in the tank, the height of the fuel at a second location in the tank and the height of the fuel at a third location in the tank. A single algorithm for determining the volume of fuel in the tank upon the receipt current values of the at least three parameters is generated from the data on the plurality of measurements. The algorithm is input into processor means arranged in connection with the vehicle. Thereafter, when the at least three parameters are measured during operation of the vehicle, and input into the algorithm, the algorithm provides the volume of fuel in the tank. In certain embodiments, the parameters are the load of the tank on a load cell at a first location, the load of the tank on a load cell at a second location, and the load of the tank at a load cell at a third location, and whereby the fuel tank is mounted to the vehicle such that it is subjected to forces along the yaw axis of the vehicle, and the first, second and third load cells are arranged between different portions of the fuel tank and the vehicle such that they are sensitive along an axis that is generally parallel to the yaw axis of the vehicle. A signal representative of the volume of fuel contained in the tank may be displayed to the driver.
In other embodiments, the parameters may be the load of the tank on a load cell at a first location, the load of the tank on a load cell at a second location, the load of the tank at a load cell at a third location, the pitch angle of the tank and the roll angle of the tank, whereby a pitch and roll angle sensor is arranged to measure the pitch and roll angle of the vehicle. When three load cells are present, they may be arranged between the different portions of the fuel tank and a portion of a common reference surface of the vehicle, the load cells being sensitive along an axis that is substantially normal to said mounting surface. To enhance the fuel quantity measurement, the specific gravity of the fuel in the tank may be determined and input into the algorithm to be considered in a determination of the quantity of fuel in the tank.
One embodiment of the apparatus for measuring the volume of a liquid in a fuel tank in a vehicle that is subject to varying external forces caused by movement or changes in the roll and pitch angles of the vehicle, comprises a fuel tank mounted to the vehicle and subject to forces along the yaw axis of the vehicle, at least three transducers each providing an output signal representative of a parameter selected from the group consisting of a pitch angle of the vehicle, a roll angle of the vehicle and a level of fuel at a discrete location within the tank, and computational means coupled to the transducers for receiving the output signals from the transducers and for processing the same to obtain a volume of fuel in the tank. The computational means comprise means for storing an algorithm representative of a derived relationship between the parameters corresponding to the output signals from the transducers and the volume of fuel in the tank and applying the algorithm using the output signals from the transducers as input to obtain the volume of fuel in the tank. The transducers may each provide an output signal representative of the level of fuel at a different discrete location within the tank. In one specific embodiment, the transducers comprise ultrasonic transducers, the tank has a non-partitioned fuel-retaining interior compartment and the transducers are arranged to measure the level of fuel at three different discrete locations within the non-partitioned interior of said tank.
Another embodiment of the method for measuring the volume of a liquid in a fuel tank in a vehicle that is subject to varying external forces caused by movement or changes in the roll and pitch angles of the vehicle in accordance with the invention comprises the steps of generating an algorithm for use on the vehicle by placing a known quantity of fuel into the tank, collecting reflected wave patterns from a plurality of ultrasonic transducers arranged on a bottom of the tank at discrete locations under various conditions from an at rest position to a driving state over a variety of road surfaces, repeatedly changing the quantity of fuel in the tank and collecting additional reflected wave patterns from the ultrasonic transducers, inputting the data concerning the quantity of fuel in the tank and the received reflected wave patterns into a neural network generating program to obtain an algorithm. The algorithm is installed onto a component in the vehicle, and then during use, reflected wave patterns are obtained from the transducers during operation of the vehicle, and inputting into the algorithm to obtain the quantity of fuel in the tank. Also, the volume of the tank may be determined by collecting reflected wave patterns from the tank in an empty condition and inputting this data into the neural network generating program.